Losses of muscular strength and muscle mass with age (sarcopenia) and gains with strength training in the elderly are well documented, but these responses vary substantially among individuals. This large interindividual variability and the fact that twin studies show that a major portion of the variance in strength and muscle mass can be accounted for by heredity, suggest that genetic factors may explain a large portion of interindividual differences in strength and muscle mass responses to aging and strength training. In a recent pilot study, we observed that a common polymorphism at the ciliary neurotrophic factor (CNTF) gene locus was a significant predictor of age-associated strength levels and that a common polymorphism at the insulin-like growth factor II (IGF-Il) gene locus was significantly associated with strength increases in response to strength training. Moreover, polymorphisms at the IGF-l, tumor necrosis factor (TNF) alpha, and IL-15 receptor gene loci showed a pattern for being associated with strength and/or muscle mass response to strength training. Therefore, this study will test our primary hypotheses in both cross-sectional and longitudinal studies, that the polymorphism at the CNTF gene locus will affect strength levels in older persons and losses in strength with age, and that the polymorphism at the IGF-II gene locus will affect strength and muscle mass responses to strength training in elderly women and men. We will also test exploratory hypotheses that polymorphisms at the IGF-l, and TNF alpha gene loci will affect losses in strength and muscle mass with age and that a polymorphism at the TNF alpha and IL-15 receptor gene Loci will affect strength or muscle mass gains with strength training in elderly women and men. Findings consistent with our hypotheses could result in identifying those most likely to need interventions for sarcopenia and the optimal manner of stratifying strength training to those benefiting the most. Conversely, identifying persons who improve their strength and muscle mass the least with strength training would allow them to focus on interventions that might be more efficacious for them.